square miles. Each building has its own grounding system. If these grounding systems are not tied
together, a potential difference on the grounding circuit for the communication cable can occur. The
idea behind grounding for noise control is to create an equipotential grounding system, which in turn
limits or even eliminates the potential differences between the grounding systems. If the there is an
equipotential grounding system and currents are injected into the ground system, the potential of the
whole grounding system will rise and fall and potential differences will not occur.
Supplemental conductors, ground reference grids, and ground plates can all be used to improve the
performance of the system as it relates to power quality. Optically isolated communications can also
improve the performance of the system. By using the opto-isolators, connecting the communications to
different ground planes is avoided. All improvements to the grounding system must be done in addition
to the requirements for safety.
Separation of loads is another method used to control noise. Figure 29.3 illustrates this point. Figure 29.3
shows four different connection schemes. Each system from left to right improves noise control.
As seen in Fig. 29.3, the best case would be the complete separation (system on the far right) of the
ADP units from the motor loads and other equipment. Conversely, the worst condition is on the left of
Fig. 29.3 where the ADP units are served from the same circuit as the motor loads.
29.3 Typical Wiring and Grounding Problems
In this section, typical wiring and grounding problems, as related to power quality, are presented.
Possible solutions are given for these problems as well as the possible causes for the problems being
observed on the grounding system. (See Table 29.2.)
The following list is just a sample of problems that can occur on the grounding system.
.Isolated grounds
.Ground loops
.Missing safety ground
.Multiple neutral-to-ground bonds
.Additional ground rods
.Insufficient neutral conductors
29.3.1 Insulated Grounds
Insulated grounds in themselves are not a grounding problem. However, improperly used insulated
grounds can be a problem. Insulated grounds are used to control noise on the grounding system. This is
208Y/120V208Y/120V 208Y/120V208Y/120V208Y/120V 208Y/120VADP UnitsAC Units
ADP UnitsAC Units
ADP UnitsAC Units
ADP UnitsAC Units208Y/120V480V480V
480V480V480V480V480VFIGURE 29.3 Separation of loads for noise control.